Electrodynamic sound reproducer



y 933- P. L. JENSEN 1,906,379

ELECTRODYNAMIC SOUND REPRODUCER Filed on. 29, 1921 //v VE/VTOE P5752 4JENSEN mfmq age of the leads carrying current Patented May 2, 1933'UNITED STATES PATENT OFFICE PETER'L. JENSEN, OFlALAMEDA, GALIFORNIA,'AssIGNon, BY MESNE ASSIGNMENTS,

T0 JENSEN RADIO MANUFACTURING COMIPANY, OF CHICAGO, ILLINOIS, A CORPO-RATION OF NEVADA ELECTRODYNAMIC souNn BEPBODUGER Application filedOctober- 29, 1927. Serial No. 229,575.

My invention relates to magnetic sound re-'producers,'andparticularly-to those of the phragm.

A further object is to provide a supporting means for a moving coilwhich will position thecoil definitely in its own plane while permittingfree movement normal to said plane. v,

Still another object of my invention is to provide a means forpreventing the breakto the moving coil.

My invention possesses other objects and valuable features, some ofwhich will be set forth in the following description of my inventionwhich is illustrated inthe drawing formingpart of the specification.- Itis to be i understood that I do not-limit myself to the showing made-bythe said description and drawing, as I may adopt varying forms of myinvention within the scope of the claims.

Referring to the drawing:

'Fig. 1 is a sectional view of a sound reproducer embodying myinvention, the plane 7 of section including the longitudinal axis of thedevice. a

Fig. 2 is a view of the same partly in section on the line 2-2 of. Fig.1.

tion, showing the elements of the coil mounting in separated position. VBroadly considered my invention comprises a coil wound on a form. Aportion of a diaphragm conforming to the form is clamped thereto by acollar. ,jecting from the collar are attached to the.

Spokes pro- 7 body of the reproducer to'position the coil lines of forceforming it is suspended a'coil which carries'the telephonic currentrepresenting the sound to be reproduced. This telephonic current-sets upamagnetic field of its own which reacts with the main field to urge thecoil in a direction normal to both field and coil. 1

If the coil be fixed to a suitable radiating system its energy' will bedelivered to the Y air. The design of such a device is directed to theend that this energy be so delivered as efficiently as possible, andthat it follow, as closely as may be, the exact wave form of theelectrical energy supplied. I

. The force acting on the coil at any instant is proportional to theproduct of the. constant field timesthe current in the movable coil. Itis evident therefore that other things being equal,'the sensitivityofthe device is directly dependent upon the .strength ofthe- If themagnet is properly'designed only a very small proportion of themagnetomotive force is expended inIthe ferro-magnetic portionsof thecircuit, the majorpart of the force going to maintain the field in theairap." 1 a b The magnetomotive force necessary to produce a givenstrength of field in thegap is directly proportional to the gap length.It can therefore readily be seen that it, is desirable to make the partof the gap not b .actually occupied the coil, just as. short as Fig. 3is a detail view, partly in axial secpossible, i..e., to reduceclearances to a minimum. At. the same time the coil must be wholly freefrom the sides of the gap, for friction at this point will produceserious distortion if it does not entirely prevent the reproducer fromfunctioning Hence a reproducer of this character, to be commerciallypractical, must be so designed that the .parts maybe held to tolerancesof the order of one thousands of an inch, and means 'must be providedfor accurately positioning coil and air gap so that the coil is freelymovable in its designed direction of motion, but is positively preventedfrommotion in other dimensions. How I accomplish this in a preferredembodiment of my invention wlll nowbe set forth in detail.

The main or constant field is provided by a winding 6 which I have showninsulated from a brass bobbin 7 by a layer 8 of fibrous material.Surrounding the winding is the ferro-magnet'ic casing 9, provided at itslower end with the inwardly projecting flange 11 which constitutes oneportion of the yoke. A plate 12 constituting the remainder of the yokeis attached to the flange by the screws 13 which are threaded into theflange. The holes in the plate thru which these screws pass aresufficiently large to allow an adjusting movement of the plate in itsown plane of several thousandths of an inch when the screws are loose. I

Riveted or otherwise rigidly fixed to the plate 12 is the core 14 whichisloosely encircled by the flange 11 and projects completely thru thecoil. The free end of this core or stud forms one of thepole piecesdefining the air gap. Theother pole piece is formed by the ring 16 whichis accurately positioned on the casing by a groove or rabbet formed inits periphery; I

A frame 17, preferably of cast aluminum, is secured to the ring polepiece by the screws .18. Lugs 19, cast integral with the frame arefastened to the brackets 21 by the screws 22, and the brackets, in turn,are screwed to the casing, thus holding the pole piece, together withthe frame and the parts attached thereto, firmly in place. It isadvantageous to have the screws 23, which secure the brackets to thecasing, pass completely thru the latter, and impinge upon the flange ofthe bobbin 7, thus preventing it from shifting in shipment or otherwise.V

Mounted upon the frame are the movable elements of the reproducer. 7These comprise the coil 24 which is wound'upon and cemented to the form26. This form may be turned from a suitable material such as bakeli te'or wound from paper, with a thickened portion provided at its outer end.The. conical diaphragm 27 is truncated and is serrated from the plane atwhich its inner diameter is equal to the outer diameter of the form, theserrations being bent outward to form a projecting flange which embracesand conforms to the thickened portion of the form.

Over the junction thus formed is pressed a spider '28 which comprises acollar with projecting spiral spokes. The spider preferably "is punchedfrom thin sheet metal, the portion forming the collar being drawnperpendicular to the plane of the spokes. Before assembly the adjacentsurfaces of collar, form and diaphragm are coated with laquer or cement,

which holds the parts permanently in place.

The spider is secured to the frame by screws 29 passing thru the outerends of the spokes. and clamping them between the washers 81, which arepreferably'of fibrous material; The leads 32 from the coil 24 aresecured to the spokes, preferably by cementing them thereto betweenlayers of thin insulation, this construction preventing the breakage ofthe leads from the constant vibration to which they are subjected, whichis a'serious source of failure lIlIIBPIOdllCGIS of this type.

Suitable means are provided at the distal portion of the frame 17 forflexibly supporting the diaphragm 27. Since this is no part of thepresent invention, it need not be shown or described herein.

The construction just described permits the ready and accuratepositioning of all of the parts. The magnet structure is first assembledwithout the diaphragm or moving parts. All of the screws fastening theassembly are set up tightly with the exception of the screws 13, whichare left loose". An annular gage is then slid over'the studpole pieceand into theorifice of the ring pole piece,'the yoke portions 11 and 12sliding to allow the stud to center accurately to permit this. Screws 13are then tightened and the gage withdrawn.

The ring pole 1.6 and frame 17 are drilled in igs, so that when thespider 28 is screwed in place the coil 24 is centered in thegap withoutfurther adjustment. The spokes of the spider, being spirally disposed,allow a considerable movement of the coil thru the gap, but effectuallyprevent motion across the gap which would permit the coil to strike thepole pieces.

It is of course to be understood ithat'in claiming the magnetic circuitcomprising the to the flange, spiral spokes on the collar, and

means for rigidly mounting the ends of the spokes to position the coil;r p

2. A sound reproducer comprising a cylindrically formed coil, adiaphragm having a projecting flange, a collar securing the coil to theflange, spokes on the collar, meansfor rigidly mounting the ends of thespokes to position the coil, and leads for the coil secured to thespokes.

3. A sound reproducer comprising a c-ylindrical' form, a coil mounted onthe form, a diaphragm having a projecting flange, a collar between whichand the form said flange is secured, spokes fixed to the collar, and

means for rigidly mounting the ends of the spokes to position the coil.

4. A sound reproducer comprising a cylindrical form having a thickenededge, a coil mounted on the form, a diaphragm having a projectingflange, anda collar between which and said thickened edge of the formsaid flange is secured.

5. A sound reproducer comprising a cylindrically formed coil, adiaphragm having 5 a serrated edge bent to form a projecting flange, anda collar securing the coil to the In testimony whereof, I have hereuntoset my hand.

PETER L. JENSEN.

